Since decoherence is a generic problem, effective error mitigation and correction are quintessential for the development of reliable quantum computation in practice.[1]}
Soon after the first quantum computation algorithms, powerful algorithms for error correction were proposed,[2]}, [3]}, [4]} typically relying on redundancy in the encoding and the measurement of syndrome operators followed by active correction of the errors.
These active methods can require a large overhead, both in terms of required information storage capacity and complexity of the actual algorithms.
For this reason, an emerging activity is on qubits with some kind of passive error resilience, often built into the system Hamiltonian.
<FIGURE>